JPH07177355A - Improvement of discharge region developing region - Google Patents

Abstract

PURPOSE: To provide a method for improving an output along with the edge of discharging area developed section. CONSTITUTION: 81 pixels of 9×9 rectangular matrix are inputted from scanning line buffers 114a and 114b to template matching blocks 116a and 116b. At the blocks 116a and 116b, video data expressing a pixel array surrounding the selected pixel are compared with the prescribed set of templates and it is determined whether these data are matched with any one of templates or not. When the data are matched, a code is generated and outputted from the block 116a or 116b, and an image forming method for the selected pixel is specifically discriminated. A block 120 generates a video signal for driving an A/O modulator. The pulse characteristics, width and position required for executing desired exposure are determined and preloaded into a PWPM look-up table (converting means) 122 for converting the pixel code into the pulse characteristics. When a video pulse is generated by the PWPM circuit of block 120, the video pulse is sent to the A/O modulator.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to apparatus for improving (or enhancing) the image area output by a digital printing system, and more particularly to pulse width in a tri-level xerographic printer. Used to drive a modulated printing exposure device,
The present invention relates to an improved system for modifying a digital image signal.

[0002]

SUMMARY OF THE INVENTION The present invention is a pulse width modulated raster output scanner (ROS) for producing tri-level latent images, such as the Xerox 4850 highlight color laser printing system. Can be used in a tri-level printing system that uses The tri-level latent image produced by such a system is developed and transferred to an output sheet or similar print medium. In tri-level or highlight color imaging, unlike conventional xerography, three charge levels are created on the charge retentive surface when exposed. Areas that are highly charged (that is, not exposed) are developed with toner, and areas that are most completely discharged are also developed, but with different colors of toner, called highlight colors. Is. The charge retentive surface is exposed at three levels: zero exposure, intermediate exposure, and full exposure.
exposure), which correspond to three charge levels. The resulting three charge levels can be developed and printed, for example black, white, and some solid colors.

The charged portion of the photoreceptor surface travels through the exposure station. That is, at the exposure station, a tri-level ROS (raster output scanner) unit exposes the photoreceptor surface and discharges the photoreceptor surface according to the output from the image source. This scan produces three distinct discharge areas on the photoreceptor, ie each area is exposed at one of three possible levels. Three
The two possible levels are (1) resulting in a voltage equal to the dark decay potential of the photoreceptor, zero exposure developed using charged area development (CAD), and (2) resulting in low voltage levels. And full exposure developed using discharge area development (DAD), and (3) intermediate exposure that produces an intermediate voltage level that is not developed by CAD or DAD, producing a background area on the print. Is. After development, the developed image is transferred and fused to a print medium using techniques commonly known in tri-level xerographic printing systems.

In the past, various methods and devices have been used to control and improve the output of ROS-based printing systems. Furthermore, several scanning techniques are known for performing image formation by tri-level exposure. A pulsed imaging scanner can be used to obtain higher spatial resolution.
The pulsed image scanner is also based on a paper by Richard Johnson et al., "Scophony Spatial Light Modulator."
(Optical Technology Vol. 24, No. 1, January and February 1985) is also referred to as a Scophony scanner.

US Pat. No. 4,347,523 discloses a general related device which uses an input signal to address a pulse width number by a corresponding pulse width selection number.

US Pat. No. 4,390,882 discloses a method for an image processing apparatus which adjusts the density of an image by controlling the on-time of a laser.

US Pat. No. 4,544,264 and US Pat. No. 4,625,222 describe improved circuits suitable for use in laser-based electrophotographic printing machines.

US Pat. No. 4,626,923 shows an image processing device for producing a halftone image, the image processing device being laser driven by both image input data and a pulse width modulation circuit. Control the on-time of the.

US Pat. No. 4,847,641 and US Pat. No. 5,005,139 disclose printing improvement circuits for laser beam printers.

US Pat. No. 4,933,689 discloses a method of improving a display image in a dot matrix format exposed by a laser to soften and produce edge contours.

US Pat. No. 4,965,672 discloses a device for varying the width and position of the pulses used to control a laser beam.

US Pat. No. 5,184,226 discloses a digital system for generating pulses from a series of data words.

A desired technique capable of obtaining a higher spatial resolution is an optical system similar to the flying spot scanner rotating polygon, laser light source, pre-polygon (pre-polygon) and post-polygon (post-polygon) optical systems. The element is to use an acousto-optic (A / O) modulator that becomes a scanner that illuminates many pixels at a given time, resulting in a coherent (coherent) imaging response. In this type of scanning system, the exposure level (s) at the imaging surface can be adjusted by controlling the drive level of the video data dependent A / O modulator. In the tri-level system, two drive levels are used, the first level is for white exposure and the second higher drive level is for DAD (discharge area development) or highlight color exposure. .

Instead of obtaining an intermediate exposure level by controlling the acoustic amplitude, using pulse width modulation in a pulsed imaging system with spatial filtering,
It is possible to generate intermediate exposures. The use of intuitive or conventional methods of pulse width modulation in which the pulses are focused on the pixels results in color text (letters, numbers, etc.) and graphics in the printed output having an "expanded" or fat appearance. Not only that, but when a digital image is printed, the duplicated copy may become so-called “jagged”. Jaggedness is most often seen along the edges of angled or curved lines.

The present invention aims to overcome the above-mentioned drawbacks of the prior art.

[0016]

In accordance with one aspect of the present invention and in the preferred embodiment, by extending or amplifying the width of the white or mid-level video pulse used to generate neighboring pixels, DAD development area (ie,
The jagged problem for angling or curved edges of highlight color areas is reduced. The exposure level resulting from the amplified intermediate pulse has the effect of extending the edges of the DAD area by an amount equal to the amount of extension of the pulse,
This reduces the jaggedness along the edges of the DAD area.

In accordance with one aspect of the present invention, in a pulsed imaging pulse width modulation printing system capable of forming a tri-level image on a photosensitive member, the discharge area developed portion on the photosensitive member is Provided a way to improve,
Color pixels are generated in response to a video pulse that is on for the complete pixel period, and background pixels are generated in response to a video pulse that is on for the middle part of the pixel period. It The improved method comprises converting a series of data words representing image pixels into a series of synthetic analog video pulses corresponding to a plurality of pixel periods, each pixel period formed on a surface of the photosensitive member. A charged image area, a discharged image area, and an intermediate discharged image area, the combined video pulse being provided to an acousto-optic modulator and used to expose an area of the photosensitive member. Modulating a laser beam to identify the subset of data words that should be modified to improve the appearance of the discharge area developed portion of the output image; modifying the video pulse corresponding to the selected data word. Modifying the selected data word in the subset by

According to another aspect of the present invention, in a pulsed imaging pulse width modulation printing system capable of forming a tri-level image on a photosensitive member, a discharge area improving (improving) a discharge area developing portion. An improved development device is provided in which color pixels are generated in response to a video pulse that is on for a complete pixel period period, and background pixels are generated for an intermediate portion of the pixel period. It is generated in response to a video pulse turning on. The improved apparatus includes a modulator for modulating a laser beam used to expose an area of the photosensitive member; means for converting the video data stream into a composite video pulse having a uniform pixel period. Each pixel period defining a composite video pulse representing a charging region, a discharge region, and an intermediate discharge region formed on the surface of the photosensitive member, the composite video pulse being applied to the acousto-optic modulator. Means for identifying a subset of the data in the stream which is responsive to the video data stream and which should be modified to improve the condition of the discharge area developed portion of the output image; and the video pulse corresponding to the selected pixel. Modifying the video data for the selected pixels in the subset by modifying.

According to an aspect of claim 1 of the present invention, color pixels are generated in response to a video pulse which is turned on for a complete pixel period, and background pixels are generated.
In a pulsed imaging pulse width modulation printing system for forming a tri-level image on a photosensitive member generated in response to a video pulse that is turned on for an intermediate pixel period period, a discharge on the photosensitive member. A method for improving area development, comprising the step of converting a series of data words representing image pixels into a series of synthetic analog video pulses corresponding to a plurality of pixel periods, wherein each said pixel period comprises Have a composite video pulse representing a charged image area, a discharge image area, and an intermediate discharge image area formed on the surface of the photosensitive member, the composite video pulse being used to expose a portion of the photosensitive member. Applied to an acousto-optic modulator for modulating the laser beam that is to be modulated and should be modified to improve the appearance of the discharge area developed portion of the output image. Identifying a subset of Tawado, by changing the video pulses corresponding to the selected data words in the subset, including the steps of changing the selected data word.

According to a second aspect of the present invention, in the aspect of the first aspect, the step of identifying a subset of the data words to be modified stores a plurality of said data words representing image pixels in memory. Is the step
Said storing data word being selected from data words representing neighboring pixels surrounding a pixel corresponding to the selected data word, said storing step, and comparing the stored data to a template set, The comparing step, wherein each template in the set has predefined data, and selecting when the stored data word matches one of the templates in the predefined template set. Identifying the generated data words as members of a subset of the data words that should be modified to improve the appearance of the output image.

According to a third aspect of the present invention, in the aspect of the first aspect, the changing step changes the exposure level for the selected pixel by generating a video pulse wider than the intermediate pulse. Thus, applying a given wide video pulse to the acousto-optic modulator, thereby producing a medium exposure level greater than the intermediate exposure and less than the full exposure.

[0022]

DETAILED DESCRIPTION OF THE INVENTION In the following description, what is referred to as color pixel or color development is generally understood to refer to the production of highlight color marks on the output medium. There are two common types of ROS: flying spot ROS and pulsed imaging ROS. As used herein, the term "data" or "data word" is intended to refer to one or more digital signals used to represent an image, such as a video signal. Furthermore, the term "video data" refers to one or more picture elements (picture elements or pi).
xel) to refer to the electrical signal that carries the image information.

FIG. 1 illustrates a pulsed imaging pulse width modulated facet tracked according to a first aspect of the present invention.
1 illustrates a ROS system. The focused beam of light from laser 80 is provided to acousto-optic (A / O) modulator 82. The control circuit 84 converts the image bitmap video data stream into an analog video data stream consisting of a plurality of pixel periods, each of the pixel periods being a charged area (black) formed on the surface of the photoreceptor 92. It has a signal content representing a discharge area (color) and an intermediate discharge area (white). The circuit 84 controls the drive level of the modulator 82.
The light output profile emanating from the modulator 82 is defined by the overlap of the acoustic pulses and the illuminating light beam from the laser 80, allowing the imaging of the individual acoustic pulses on the photoreceptor 92. In the high-speed scanning direction, the anamorphic pre-polygon optical system 86 uses the A / O modulator 8
The Fourier transform of the light pulse emitted from 2 is performed, and the Fourier profile is projected on the surface (facet) 87 of the rotating polygon 88. The polygon 88 is arranged on the rear focal plane of the post-polygon (following the polygon) optical system 90 and the front focal plane of the pre-polygon optical system 86. The RF frequency used to excite the modulator 82 is swept by the surface tracking circuit 81 and the RF drive circuit 83 in synchronism with the scan across the photoreceptor, resulting in a Fourier profile of the rotating polygon 88. It remains in the center on the face 87. The size of the zero-order spot in the plane depends and is inversely proportional to the size of the beam at the modulator, and so is the diffractive order.

As polygon 88 rotates, the optical image of the acousto-optic video pattern is swept across the surface of photoreceptor 92 after passing through post-polygon optics 90. The motion of the acoustic image on the surface of the photoreceptor, which would otherwise blur the optical image, is offset by balancing the speed of the acoustic and scan with the magnification of the pre-polygon and post-polygon optics, resulting in the received light. The acoustic image remains stationary on the body. The imaging line is exposed at three exposure levels: zero, medium, and full. The intermediate (white) exposure level results in a spatially narrow optical pulse exiting modulator 82, narrowed in pulse width, filtered by surface 87 to result in a low and uniform exposure at photoreceptor 92. Obtained from the video signal.

[0025] Typically, the video data used to drive the ROS is clocked such that the time each pixel is exposed-hereafter referred to as the pixel clock time-is the same. In addition, the video data used to generate the video signal pulses that drive the modulator is
It is synchronized with the movement of the imaging surface in the ROS and slow scan directions, which allows a particular portion of the video data to address the appropriate portion of the image surface. The synchronization of the video data, the video pulses generated from the video data, the ROS and the image plane is achieved by using a system clock which corresponds (corresponds) to the speed at which pixels have to be exposed on the image plane. It Faster clocks provide higher resolution within the video pulse stream, but also higher frequencies, resulting in increased cost due to faster hardware in the video processing path. Therefore, the present invention improves (enhances) an image without requiring an increase in clock frequency.
Ask to do.

2A to 2C and 3A to 3C.
(D) represents the xerographic system's response to a medium exposure that falls between an intermediate or background (white) exposure level and a full (color) exposure. It will be appreciated that xerography does not produce well with large areas of medium exposure, but xerography is for medium exposed pixels adjacent to fully developed and fully exposed pixels or binary pixels. Responds in a stable and characteristic way. For example, FIGS. 2A-2C show how a xerographic process can be performed when the media exposure is adjacent to a pixel that is fully exposed (ie, a color pixel in a color DAD system). To respond to.
More specifically, FIG. 2A shows a 2 pixel wide vertical line, and FIG. 2C shows a 3 pixel wide vertical line, both of which are complete by ROS. After exposure, it is developed in highlight color. On the other hand, FIG. 2B shows the gist of the present invention, in which the medium exposure pixel is used to slightly expand the color line having a width of 2 pixels so as to achieve an intermediate line width. is there. The median exposure shown along the right edge in FIG. 2B was caused by partially stretching (extending) the edge of the fully developed area into the median pixel. When the medium exposure is changed from white to the fully discharged highlight color, the edge shifts further to the medium pixel area. Thus, the media exposure adjacent to the fully exposed and developed area provides a means of producing a series of line widths intermediate to the single pixel addressability of the imager.

Similarly, the line density expressions of FIGS. 3A to 3D show a phenomenon depending on FIG. 2B. Figure 3
2A and 2D show toner density curves for color lines of 2 and 3 pixel widths shown in FIGS. 2A and 2C, respectively. FIG. 3B shows the charge density produced on the photoreceptor by the ROS such that the median pixel produces a two pixel wide color line adjacent to the right. On the other hand, FIG. 3C shows the blurred result or response of the xerographic system compared to the charge density profile of FIG. 3B, where the developed toner density of FIG. The intermediate exposure of the median pixel area along the right side effectively extends the edge of the two pixel wide color line to the right, as shown as

Using the known imaging response of a xerographic system to medium exposure level, FIGS. 4A-4C show how to use medium exposure (M). , Can show that the jagged edges that appear in a typical 300 spi printing system can be smoothed. As will be described below, the medium exposure (M) includes 1/4 (M ₁ ), 1/2 (M ₂ ) and 3 /
Used to move the line edge by 4 (M ₃ ). For example, as shown in the enlarged view of FIG.
Given a digital image of a slanted line, the present invention seeks to improve the output of the line so as to smooth the jagged edges in that line. To achieve edge smoothing, the present invention monitors the printed image data to identify the presence of "jagged" in the image signal stream. Then, varying levels of medium exposed pixels are added to the jagged area, indicated by reference numeral 15 in FIG. 4B, to slightly expand or contract the edges of the sloped lines in the particular area. Thus, a median exposure level M ₃ is generated for a pixel location if the maximum expansion of the edge is required, and a media exposure level M ₃ if only a slight expansion of the edge is required. ₁ is used. The xerographic process then merges or blurs the medium level pixels to produce a slanted line edge as shown in Figure 4C.

Referring to FIG. 5, the system used to accomplish the above-described steps will be described. In this embodiment, pulse width, position, and amplitude modulators (pulse modulators) are used to form video pulses responsive to video data representing the image to be printed. The width and position of the pulse within the pixel clock time Δ can be changed separately, ie the leading and trailing edges of the pulse can be independently delayed in various ways. In the standard mode of operation, pulses are generated in response to the information in the corresponding data word, as disclosed in US Pat. No. 5,184,226.

The configuration of the image enhancement substrate 110 that implements the previously described aspects of the present invention will be described with reference to FIG. The basic functions of the image enhancement board 110 are (1) provide a scan line buffer for image data; (2) perform template matching on the buffer data; (3) arbitratio.
n) circuit is provided; (4) PWPM (Pulse Width and
Position Modulated) look-up table selection circuitry is enabled; (5) PWPM electronics are provided to generate the video pulses required to drive the acousto-optic modulator 82 of FIG. is there. Note that there are two channels on the image enhancement board 110, one for handling black image information and the other for handling color image information. Since each channel is processed (processed) independently, it is understood that, by design, the input video will not have overlapping states where pixels are listed as black and highlight color.

The scan line buffers 114a and 114b have the effect of storing a complete scan line or raster of video data, the number of scan lines being preferably nine, or
Ten lines are preferred if possible, so that nine lines are available while the next line is loaded into the tenth line buffer. From the scan line buffer, 81 pixels in the 9 × 9 square matrix are input to the template matching blocks 116a and 116b. In the preferred embodiment, the functionality of the template matching blocks 116a and 116b is determined by the application specific integrated circuit (ASI).
Provided by C). Referring to FIGS. 6A and 6B, in a template matching block, video data representing a 9 × 9 array 150 of pixels surrounding a selected central pixel 152 is stored in a predetermined set of templates, for example, in FIG. B) template, compared to its pixel pattern of the color image (ie from buffer 114b)
Determines if it matches one of the templates in the set.

To identify digital image areas that require image enhancement to reduce half-bitting so as to more accurately reproduce curved or beveled edges in the image. In addition, many technologies are available. The present invention utilizes a predetermined set of templates to search for regions that have the required set of "on" and "off" pixels in at least a portion of the 9x9 region 150. More specifically, the template matching block determines the required “on” or color pixel 162 in array 160, shown in black in FIG. 6B, at the location of the corresponding pixel in image array 150. Compare against. Assuming that all required “on” pixels of the template match, reference numeral 164
The “off” or white pixels shown by and shown in white space are then compared in a similar manner. In FIG. 6B, the shaded (hatched) pixel position, for example, position 1
66 indicates a "no care" position where there is no significance in comparing the output levels of the pixels. If no template match was confirmed, the output of the ASIC in template matching block 116 is set to 0 if the center pixel is white and 1 if the incoming pixel is black or color. Is set to. This preserves the level (black or color) of the input image even in unmatched situations.

Once the templates are matched, a code is generated and output from the template matching block 116a or b to output the center pixel, pixel 15
The method of imaging 2 is specifically discriminated. A 3-bit value is output from the template matching block to generate the five possible output levels shown in FIG. 4B. For example, the output code is 0 for white pixels.
00h, color pixel is 111h, M ₁ is 001h, M ₂
It is possible is 010h and M _3, is 011h.

Each channel on the image enhancement substrate is processed independently. As a result, both the black and color channels may assign values to the same pixel. This situation is resolved at arbitration block 118. In one embodiment, the arbitration circuit may be a look-up table that accepts the code output by the two template matching blocks 116a and 116b as two inputs. In fact, the function of the arbitration block enables black output (zero exposure), while color output (full exposure) is not possible due to the invisible color spots in the black areas. However, in some applications the arbitration block may be required to allow the output of color pixels.

The PWPM circuit, block 120, produces a video signal that drives an acousto-optic modulator (not shown). From the modeling and printing characteristics, the pulse characteristics, widths, and positions required to perform the desired exposure are determined and used to convert the pixel code into pulse characteristics, as indicated by the PWPM lookup table 122. Preloaded. As implemented here, the conversion means comprises four RAM look-up tables, each codeword indicating an address therein. In the preferred embodiment, a pair of 256 × 4 ECL RAM look-up tables are used to generate a pulse attribute word for each pulse attribute required to be controlled.
More specifically, the PWPM circuit 120 sends a code to the look-up table 122 and then receives a signal indicating the width, position, and state (reverse or normal) of the corresponding pulse. In one embodiment, width and position can be characterized as a pair of timing delays that identify the beginning and end of a pulse with respect to the pixel period. further,
The embodiment shown in FIG. 5 further comprises two or more sets of PWPM lookup tables, the lookup table to be used being selected in response to an external signal interpreted by the PWPM lookup table selection block 126. It Video pulse is PWPM in block 120
Once generated by the circuit, the video pulse has the form shown in FIG.
It is sent to the acousto-optic modulator 82 indicated by.

As shown in the schematic diagrams of FIGS. 7A-7C, at least conceptually, the video signal used to drive the acousto-optical variator is fed through a series of additi.
ve part). For example, in FIG.
(A) represents the video signal or pulse train required to generate a 2-pixel wide color (eg, red) line running perpendicular to the fast scan imaging direction.
The pulses are shown to lie within continuous and uniform pixel periods with width Δ. Therefore, in the DAD system, pixel positions C ₁ and C ₂ represent color pixels (complete exposure within a pixel period), and W _{1 to} W ₄ are white pixels (about 2 pixels).
(Intermediate exposure that is on for one-half cycle). More specifically, the signal of FIG. 7A is conceptually divided into two parts. The two parts are the periodic parts filtered or blurred by the special filtering properties of the ROS to produce a uniform intermediate exposure level, as shown in FIG. (C) of the pixel position C ₁
And a positive part which is blurred to form color lines by being added to the periodic part in the region of C ₂ . The technique used to form the medium exposed pixels of the present invention by applying the same analysis method is illustrated in the remaining figures.

In an embodiment of the invention, the pulse used to produce the modified gray or medium exposure as a result of the template match produces a white pixel adjacent to, ie next to, the color pixels of the line. Generated by extending the width or duty cycle of the pulse used for. Similarly, reducing the portion of the video pulse associated with a color exposure will produce a medium exposure rather than a full exposure. It will be appreciated that the color and white pulse modifications are independently selected, but the resulting video pulse streams are equal in that they both produce medium exposure levels. The difference is that if the pulse width of the white pixel is expanded, the neighboring colored region is expanded moderately, and if the pulse width is reduced for the colored pixel, the colored region is contracted moderately.

As shown in FIG. 8A, the white exposure pulses W _{1 to} W ₄ are preferably aligned at the beginning of the pixel period. Thus, to expose adjacent white pixels W ₂ and W ₃ by the additional amounts shown by T ₁ and T ₂ , respectively,
By adding to the pulse width at the trailing edge, broadening of the white exposure pulse can be achieved. The expansion results in a medium level exposure that effectively expands the line width as a result of the additional exposure in pixel periods W ₂ and W ₃ , as shown by the corresponding decomposition in FIG. 8B. By varying the expansion amount (T) of the white exposure pulse and depending on the response of the xerographic system to the intermediate exposure level described above, the positive separation shown in FIG. Blurring produces a color line having a width slightly greater than two pixels wide. Thus, in response to the template match, a video pulse is generated to slightly extend the edge of the color or discharge area developed portion of the output image or to enlarge the color or discharge area developed portion of the output image. In addition, the amount of edge expansion depends on the particular template matched so that the edges of the discharge area developed portion are enhanced or improved and the jagged appearance is reduced.

As shown in FIG. 10A, the width and position of the pulse 52 within the pixel clock time 54, previously referred to as Δ, is separate and independent for the leading edge delay 56 and trailing edge delay 58 of the pulse 52. Can be independently varied by the globally variable delay. The leading edge delay 56 is defined from the beginning 60 of the pixel period to the leading edge 50 of the pulse. The trailing edge delay 58 is defined from the beginning 60 of the pixel period to the trailing edge 62 of the pulse. In standard operating mode, the pulse 52 is generated in response to the information in the corresponding data word, as shown in US Pat. No. 5,184,226.

Also in the preferred embodiment shown in FIG. 9A, the pulses used to generate the media exposure as a result of template matching are shown as altering the white or intermediate pixel exposure adjacent to the color pixel. Be done. However, in the present embodiment, the intermediate exposure is performed by extending the total exposure pulse in the white pixel period by adding the second pulse (S ₁ ) in the pixel period, as shown in FIG. Is generated. Unlike the pulse extension method of FIG. 8A, this preferred embodiment extends along the pulse portion used to form the color line. This results in a more symmetrical extension of the line as compared to the embodiment shown in Figure 8A.

More specifically, the extension pulse S ₁ is adjusted at the end of the pixel period W ₂ so that the period C ₁
It will be adjacent to a pulse that extends completely across. On the opposite side of the 2-pixel wide line, the extended pulse S ₂
Are added at the end of the partial (approximately half cycle) pulse used to provide the intermediate exposure level. Again, because the position and width of the video pulse can be controlled, and then the pulse [FIG. 10 (A)] is inverted to produce a pair of complementary pulses [FIG. 10 (B)]. The pulse characteristics output from the PWPM look-up table of FIG. 5 produce a media exposure level. As shown in FIG. 10B, complementary or reverse pulses 70 and 72.
Are aligned to pixel clock boundaries 60 and 61, respectively. In addition, the medium exposure level is the complementary pulse 70.
And 72 is inversely proportional to the inactivity time.

As described above, the medium exposure level between the intermediate exposure required for non-development and the complete exposure required for discharge area development (DAD) is the decomposition portion of FIG. 9B. As shown in, the area where the color marking particles are developed in the DAD system is widened. Figure 9
(B), the width of the narrow pulse in pixel positions W ₂ and W ₃ represents an additional amount to the intermediate exposure level used to generate the white pulse in the tri-level development system.

In summary, the present invention is an apparatus for enhancing output along the edge of a discharge area developed portion in a tri-level imaging system that uses pulse width and position modulated ROS for exposure. The invention is used to drive a ROS so as to extend the developed portion by a selected amount and reduce the digitization-induced phenomena (jagged edges, etc.) that appear in the printed image. Allows the signal to be identified and selectively modified. Expansion of the discharge area developed areas is accomplished by expanding the width of the exposure pulse in adjacent areas or by adding separate exposure pulses to allow development within a portion of those areas. Similarly,
The area of the discharge area development portion can be reduced by treating pixels that are "on for a complete pixel period period" as mid-level pixels or white pixels with additional pulses that can be reduced in width. It is possible.

[0044]

EFFECTS OF THE INVENTION The method for improving the developed portion of the discharge area of the present invention solves the problem of jaggedness in the output image and improves the appearance of the image.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a pulsed imaging pulse width modulated surface-to-tail raster output scanning (ROS) system.

2A-2C show the response of a xerographic printing system using discharged area development.

3A-3D are graphs showing line density versus distance for a xerographic printing system that uses discharge area development to generate lines.

4A-4C show an application of the present invention for producing a median exposure used to smooth and print jagged edges appearing in a digital image.

FIG. 5 is a block diagram illustrating components of an embodiment of an image enhancement incorporating the present invention.

FIG. 6A is a schematic diagram showing an array of pixel positions used by the present invention in a template matching operation, and FIG. 6B is a schematic diagram showing an example of a template used in a preferred embodiment of the present invention. It is a figure.

7 (A)-(C) are plots of a two pixel wide highlight color (eg, red) field distribution generated on a white background using the well-known tri-level printing process. It is shown in the graph.

FIGS. 8A and 8B are graphs showing the division of an electric field showing an embodiment of the present invention for generating medium level pixels.

9A and 9B are graphs showing electric field division showing another embodiment of the present invention for generating medium level pixels.

10 (A) and 10 (B) are schematic diagrams of pulses used in the present invention.

[Explanation of symbols]

 80 Laser 82 Acousto-optic (A / O) modulator 83 RF drive device 84 Control circuit 86 Pre-polygon optical system 88 Polygon 90 Post-polygon optical system 92 Photoreceptor 110 Image improvement substrate 114a, b Scan line buffer 116a, b Template matching block 118 Arbitration circuit 120 PWPM circuit 122 PWPM lookup table 126 PWPM lookup table selection block

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H04N 1/23 103 Z 1/405 H04N 1/40 B (72) Inventor Robert P. Roche New York, USA 14609 Rochester Grand Avenue 481 (72) Inventor Martin E. Banton United States New York 14450 Fairport Timber Lane 22 (72) Inventor Ronald E. Jodhine United States New York 14534 Pittsford Park Acre Rod 56

Claims (3)

[Claims] 1. A color pixel is generated in response to a video pulse that is on for a complete pixel period period, and a background pixel is responsive to a video pulse that is on for an intermediate pixel period period. A method for improving discharge area development on a photosensitive member in a pulsed imaging pulse width modulation printing system for forming a tri-level image on a photosensitive member, the method comprising: Converting the data word into a series of synthetic analog video pulses corresponding to a plurality of pixel periods, wherein each pixel period comprises a charged image area formed on the surface of the photosensitive member, Discharge image area,
And with a composite video pulse representing the intermediate discharge image area,
The composite video pulse is applied to an acousto-optic modulator for modulating the laser beam used to expose a portion of the photosensitive member and is modified to improve the appearance of the discharged area developed portion of the output image. Identifying the subset of data words to be processed, and modifying the selected data word by modifying the video pulse corresponding to the selected data word in the subset. . 2. The step of identifying a subset of the data words to be modified is the step of storing a plurality of said data words representing image pixels in a memory, said stored data words being the selected data words. Said storing step selected from data words representing neighboring pixels surrounding the pixel corresponding to the word, and comparing said stored data to a template set, each template in said set being defined data And comparing the stored data word with one of the templates in a predefined template set to improve the appearance of the output image with the selected data word. Identifying as a member of the subset of data words that should be modified to The method of non claim 1. 3. The altering step produces a video pulse wider than the intermediate pulse, and the given wide video pulse to the acousto-optic modulator so as to vary the exposure level for the selected pixel. Providing, thereby producing a medium exposure level greater than the intermediate exposure and less than the full exposure.